Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

846
FXUS63 KLOT 191137 CCA
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
514 AM CST Fri Dec 19 2025...CORRECTED.

.KEY MESSAGES...

- Lingering snow showers and flurries are expected early this
  morning. While little to no snow accumulation is expected,
  some slick spots may develop on roads where liquid remains
  from yesterday`s rain.

- Blustery conditions are expected today before temperatures
  moderate on Saturday with highs back above freezing.

- After a see-saw in temperatures this weekend, a warming trend
  will take hold next week.

&&

.DISCUSSION...
Issued at 252 AM CST Fri Dec 19 2025

Through Saturday:

An upper trough continues to pivot over the Great Lakes this
morning with its associated 983 mb surface low traversing across
northeast Ontario. These features have continued to support
period of convective snow showers and flurries across northern
IL and northwest IN overnight, but they should be coming to a
conclusion over the next 2 hours or so as drier air filters in
from the west. In the meantime, expect the more robust snow
showers to result in some locally reduced visibility and maybe
up to a couple tenths of accumulation. Given the short duration
of the showers at any one location (15-30 minutes at most) and
likely presence of road treatments, suspect travel impacts
should be minimal. However, anywhere lingering moisture from
rain yesterday that resides on roads may be frozen and lead to
patchy slick spots. So as a precaution be sure to allow a few
extra minutes for the morning commute today.

Otherwise, the main forecast item of note today will be the
gusty west-northwest winds gusting around 30-35 mph. While the
strongest winds are expected to occur through daybreak, lighter
(20-25 mph) winds will persist through this afternoon making
temperatures feel notably cooler than what the thermometer reads
(wind chills in the lower teens). Speaking of temperatures,
highs today will only top out in the lower to mid-20s due to
continued cold advection.

Heading into tonight, winds will ease and turn southerly as a
surface high moves across the Lower Mississippi Valley. These
southerly winds will allow temperatures to gradually warm
through the night with readings forecasted to be near 30 by
daybreak Saturday. At the same time, another shortwave trough
will be pivoting into the northern Great Lakes which will
develop another surface low over the UP of MI and cause winds to
increase in speed with 20-30 mph gusts starting late tonight
and persisting into Saturday.

As far as precipitation goes, the shortwave looks to be
somewhat moisture starved especially with southward extent so
any precipitation looks to stay in WI and MI. That said,
forecast soundings do get close to becoming saturated late
Saturday morning through mid-afternoon which may result in a
period of light precipitation near the IL-WI line. With surface
temperatures expected to be in the mid to upper 30s it looks as
if precipitation should fall as rain if it occurs, but some
snowflakes could mix in at times if temperatures aloft cool
sufficiently. Regardless, no accumulation or travel impacts are
expected.

Yack


Saturday Night through Thursday:

The weather in the Great Lakes on Sunday will be defined by a
passing surface high pressure system leading to sunny skies and
light to nearly calm winds. With our area residing on the back
edge of a pool of seasonably cool low-level air (on the backside
of a departing upper-level trough), highs Sunday afternoon will
top off in the mid 20s to lower 30s, coolest near the Wisconsin
state line.

Monday onward, anomalous upper-level blocking south of Alaska will
facilitate aggregate troughing along Pacific Coast, enabling a broad
region of quasi-zonal flow generally centered along the US/Canadian
border. With the mean position of the upper-level jet to our north,
the stage will be set for a prolonged period of above-average
temperatures. Highs are expected to rise 5 to 7 degrees each day,
starting in the upper 30s to lower 40s on Monday rising to the low
to mid 50s (if not warmer) by Christmas.

Chances for precipitation next week will be tied to WAA-
regimes ahead of passing upper-level shortwaves embedded in the
quasi-zonal flow centered to our north. At this point, am
seeing two windows to watch for such WAA-driven precip, with the
first Sunday night into Monday and the second Christmas Eve
into Christmas. With the former (Sunday night into Monday), low-
level temperature profiles would be supportive of a wintry mix
as the precipitation type. However, forecast soundings depict a
notable pocket of dry air near the ground, which may end up
limiting any precipitation from occurring. With the latter
(Wednesday night into Thursday), a more formidable push of low-
level moisture (dew points rising into the lower 50s) may lead
to fairly damp conditions characterized by drizzle and
intermittent showers. At this point, blended NBM guidance only
advertises around 10% chances for measurable precipitation with
either system, which seemed fine for now.

Borchardt

&&

.AVIATION /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 514 AM CST Fri Dec 19 2025

Intermittent flurries and snow showers will continue through the
next few hours as broken MVFR stratus (with in-cloud
temperatures squarely in the DGZ) gradually erodes from west to
east. The RAP 850mb relative humidity was used as a proxy for
the back edge of the stratus, with medium to high confidence
for FEW to SCT coverage by 14-15Z at all terminals. As the low-
level pressure gradient gradually relaxes in the wake of a
departing low pressure system, northwest winds gusting at around
30 kt at press time should slowly ease through the morning.

A surface pressure ridge will slide through the terminals by
early afternoon, causing winds to drop off in magnitude (to 10kt
or less). Wind direction will back westerly to southwesterly
through the daylight hours, and then south to southeasterly at
around sunset. Confidence in wind trends (decreasing magnitude
and varying wind direction) is high.

Yet another storm system will race through the Upper Great Lakes
tonight and induce the development of a strong low-level jet.
While the tightening low-level pressure gradient should allow
for occasional surface gustiness by midnight (mostly 20-25kt,
though perhaps occasionally as high as high as 30kt at Chicago
sites), flow at 2kft of 50 to locally 60kt renders high
confidence that LLWS criteria will be met through mid-morning.

A cold front with a northwesterly wind shift will approach
ORD/MDW toward the end of the 30-hour TAF window. A sprinkle or
snowflake may accompany the front, as well.

Borchardt

&&

.MARINE...
Issued at 352 AM CST Fri Dec 19 2025

Westerly gales of 35-40 kts will persist through this morning,
especially east of Gary, IN. As a result the Gale Warning
remains in effect until 9 AM CST for the Illinois nearshore and
12 PM CST for the Indiana nearshore for this threat. While winds
will diminish this afternoon, gusts of 20 to 25 kts are expected
to linger into this evening and thus have issued a Small Craft
Advisory for these winds and lingering waves on the Indiana
shore.

Finally, another storm system will move into the northern Great
Lakes late tonight into Saturday which will force another cold
front through Lake Michigan. With warmer air expected to move
over the lake ahead of the front, uncertainty remains as to how
deeply the atmosphere will mix and how frequent gale force gusts
will be. Therefore, have opted to handle this period with
another Small Craft Advisory for 30 kt winds but will mention
the potential for a few gales within. If confidence grows in
frequency of gales tonight a Gale Warning may be needed.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Warning until 9 AM CST this morning for Winthrop Harbor
     IL to Gary IN.

     Small Craft Advisory from 9 AM this morning to 2 PM CST this
     afternoon for Winthrop Harbor IL to Gary IN.

     Small Craft Advisory from midnight tonight to 3 PM CST
     Saturday for the IL and IN nearshore waters.

     Gale Warning until noon CST today for Gary to Burns Harbor IN-
     Burns Harbor to Michigan City IN.

     Small Craft Advisory from noon today to 8 PM CST this evening
     for Gary to Burns Harbor IN-Burns Harbor to Michigan City
     IN.

&&

$$

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